The present invention relates to methods and compositions for reducing the water permeability within a subterranean formation, particularly within a proppant pack or a gravel pack, using a relative permeability modifier, and, more specifically, to methods and compositions for treating at least a portion of a subterranean formation using a relative permeability modifier coated on a particulate material.
The unwanted production of water, including brine, from hydrocarbon-producing wells constitutes a considerable technical problem and expense in oilfield operations. When a subterranean formation contains water in significant amounts, water's higher mobility often allows it to flow to the well bore by way of natural and manmade fractures and high permeability streaks. If the ratio of recovered water to recovered hydrocarbons becomes sufficiently large, the cost of separating the water from the hydrocarbons and disposing of it can become a barrier to continued production. This can lead to abandonment of a well penetrating a subterranean formation, even when significant amounts of hydrocarbons remain therein.
In order to reduce the undesired production of water from hydrocarbon-producing subterranean formations, aqueous-soluble polymer systems containing crosslinking agents have been used in the art to enter water-containing zones of the formation and block the flow of water therefrom. Selective placement of these crosslinked polymers in a subterranean formation and stability therein represent significant technical challenges that have somewhat limited their use. A more recent strategy to reduce water production from a subterranean formation has been to use agents known as relative permeability modifiers (RPMs). Such RPMs are capable of significantly reducing the flow of water within a subterranean formation while having a minimal effect on the flow of hydrocarbons. The use of RPMs does not generally necessitate the use of zonal isolation techniques that are often employed with crosslinked polymers.
While RPMs can overcome the necessity for selective placement in a subterranean formation, it may still prove advantageous to place RPMs in a desired zone of a subterranean formation in order to more efficiently focus their effects therein. For example, placement of a RPM directly in a water-producing zone of a subterranean formation can allow for more efficient use of the RPM where its effects are directly needed, rather than when it is dispersed throughout the formation, possibly in zones where it is not needed. More specifically, some formations such as, for example, shale formations, may require excessively large volumes of the RPM be used to fully contact the formation or to reach an effective RPM concentration in a target zone. When only a portion of the subterranean formation needs to have its water permeability reduced, this represents an inefficient use of the RPM. From an economic standpoint alone, it would be beneficial to more selectively place a RPM in a subterranean formation in order to reduce the amount of material needed for effective formation treatment.